Enzymes are primarily protein and act as biological catalysts in a wide variety of vital metabolic processes. Simple enzymes are comprised of protein only and conjugated enzymes are those which are comprised of both a protein and a non-protein portion. All enzymes aid in biochemical processes through their ability to bind to their respective substrates and lower the amount of activation energy required for a metabolic reaction to occur.
Like other catalysts, enzymes remain unaltered after enabling a biochemical reaction. When enzymes bind with their respective substrates, they form an enzyme-substrate complex. This creates an active site in which a biochemical reaction can take place that was not possible prior to the formation of the enzyme-substrate complex.
Nearly all of the biochemical reactions that take place within a cell require enzymes in order for those reactions to occur at a rate of speed that enables life to continue. The ability of enzymes to increase reaction speeds by lowering the activation energy levels can also be described as lowering the kinetic barrier of a chemical reaction. The majority of enzyme-assisted reaction speeds are millions of times faster than the speeds of comparable unassisted biochemical reactions.
Enzymes differ from most other catalysts by being highly specific to the types of substrates they will bind to. There are about 4,000 known biochemical reactions that enzymes catalyze. Some enzyme processes are used for commercial purposes, such as synthesizing antibiotics and breaking down clothing stains in laundry products.